[PATCH] D48111: [JumpThreading] Don't try to rewrite a use if it's already valid.

[Michael Zolotukhin via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL335675: [JumpThreading] Don't try to rewrite a use if it's already valid. (authored by mzolotukhin, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D48111?vs=151079&id=152982#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D48111

Files:
  llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
  llvm/trunk/test/Transforms/JumpThreading/PR37745.ll


Index: llvm/trunk/test/Transforms/JumpThreading/PR37745.ll
===================================================================
--- llvm/trunk/test/Transforms/JumpThreading/PR37745.ll
+++ llvm/trunk/test/Transforms/JumpThreading/PR37745.ll
@@ -0,0 +1,19 @@
+; RUN: opt -jump-threading -verify-each -S -mtriple=x86_64-- -o - %s
+
+define void @foo() {
+entry:
+  br i1 false, label %A, label %B
+
+A:
+  %x = phi i32 [ undef, %entry ], [ %z, %B ]
+  br label %B
+
+B:
+  %y = phi i32 [ undef, %entry ], [ %x, %A ]
+  %z = add i32 %y, 1
+  %cmp = icmp ne i32 %z, 0
+  br i1 %cmp, label %exit, label %A
+
+exit:
+  ret void
+}
Index: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
@@ -2009,6 +2009,14 @@
       PredTerm->setSuccessor(i, NewBB);
     }
 
+  // Enqueue required DT updates.
+  DDT->applyUpdates({{DominatorTree::Insert, NewBB, SuccBB},
+                     {DominatorTree::Insert, PredBB, NewBB},
+                     {DominatorTree::Delete, PredBB, BB}});
+
+  // Apply all updates we queued with DDT and get the updated Dominator Tree.
+  DominatorTree *DT = &DDT->flush();
+
   // If there were values defined in BB that are used outside the block, then we
   // now have to update all uses of the value to use either the original value,
   // the cloned value, or some PHI derived value.  This can require arbitrary
@@ -2018,16 +2026,16 @@
   for (Instruction &I : *BB) {
     SmallVector<Use*, 16> UsesToRename;
 
-    // Scan all uses of this instruction to see if it is used outside of its
-    // block, and if so, record them in UsesToRename. Also, skip phi operands
-    // from PredBB - we'll remove them anyway.
+    // Scan all uses of this instruction to see if their uses are no longer
+    // dominated by the previous def and if so, record them in UsesToRename.
+    // Also, skip phi operands from PredBB - we'll remove them anyway.
     for (Use &U : I.uses()) {
       Instruction *User = cast<Instruction>(U.getUser());
       if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
         if (UserPN->getIncomingBlock(U) == BB ||
             UserPN->getIncomingBlock(U) == PredBB)
           continue;
-      } else if (User->getParent() == BB)
+      } else if (DT->dominates(&I, U))
         continue;
 
       UsesToRename.push_back(&U);
@@ -2046,12 +2054,6 @@
       SSAUpdate.AddUse(VarNum, U);
   }
 
-  DDT->applyUpdates({{DominatorTree::Insert, NewBB, SuccBB},
-                     {DominatorTree::Insert, PredBB, NewBB},
-                     {DominatorTree::Delete, PredBB, BB}});
-
-  // Apply all updates we queued with DDT and get the updated Dominator Tree.
-  DominatorTree *DT = &DDT->flush();
   SSAUpdate.RewriteAllUses(DT);
 
   // At this point, the IR is fully up to date and consistent.  Do a quick scan


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